There is a need to control the infestation of Zebra mussels, and other mollusks, which attach to inner walls of water flow passages such as pipework and other power plant components which carry water for cooling and other purposes. These mollusks and their larvae thrive in warm, non-turbulent water-flow areas in components such as pipework, and colonies are formed by layers of mollusks which attach to each other. Eventually, if left uncontrolled, the mollusks substantially impede or completely block the flow of water through the pipework or equipment.
A prior art method of dealing with this problem is to use chemical control agents where chemical substances are locally introduced into the water to kill the mollusks and/or their larvae. This, however, raises environmental problems, can be expensive, and there is a problem of localizing the chemical control agent to areas where control is most needed while avoiding areas where the chemical agents may do damage to desirable aquatic flora and fauna.
Another method used is to increase the temperature of the water flowing through the equipment to a temperature at which the mollusks and/or their larvae cannot survive, i.e., for Zebra mussels, greater than about 90.degree. F., preferably greater than 95.degree. F. for maximum effect. However this must be done for a period of a few hours, depending upon the temperature, and can cause power plant output to decrease. Alternatively, one may direct hot water or steam to selected areas for desired killing patterns, however this can be complex and is best suited for large components because of accessibility.
A common characteristic of these mollusk mitigation treatments is that the treatment must be performed from the inside of a pipe or component where the mollusks are accumulated. Therefore, in many cases accessibility limits the utilization of mechanical methods for mollusk abatement. Moreover, the extremely large quantities of water involved in many power plant applications (such as condenser cooling water), makes water treatments, including chemical treatment, exceedingly expensive. In the case of hot water treatments, it is often difficult to reach the requisite temperature. Environmental restrictions on plant effluents may also severely restrict the treatment chemicals and concentrations which may be used, making them less effective.
In commonly assigned U.S. Ser. No. 07/510,109, filed Apr. 16, 1990 now abandoned "Method of Reducing Microbiologically Influenced Corrosion," in the name of Norris Hirota, there is disclosed a method for treating microbiologically induced corrosion of metals in systems of power plants or other facilities which carry liquids which are capable of supporting microbial activity.
It is an object of the present invention to provide a method for removing mollusks and/or their larvae from structures having surfaces exposed to the aquatic habitat of the mollusks and their larvae, without the use of chemical treatments or a large volume of heated water or steam.
It is yet another object of the present invention to provide a method for preventing the growth of mollusks and/or their larvae in equipment whereby the equipment may be periodically purged of growth of mollusks and/or their larvae by localized heating of the pipework, or other equipment to which the mollusks attach.
It is another aspect of the present invention to provide a method for controlling the temperature, frequency of exposure and period of exposure of the mollusks and larvae to the heated equipment according to the present invention.